Aromatic polyimide (aramid) fibers, for example, Kevlar®, are well known in the art. Aramids are polyamides wherein at least 85% of the amide (—CONH—) linkages are attached directly to two aromatic rings. Aramids have high tensile strength and are flame and heat resistant, which makes them particularly suited to be formed into fabrics usable as protective clothing, and for many other uses.
Aramids are known to be difficult to dye. Further, aramid fibers (e.g., Kevlar®) will degrade and deteriorate at high temperatures under acidic conditions, such as those used in dye baths.
Accordingly, there is a need in the art for dyeing additives to prevent degradation of aramid fibers during the dyeing process, even at high temperatures, and to improve properties of the dyed fiber, such as depth, levelness, yarn count, and single end strength.